v0.15.0 – robust edge case handling

[Moonbase59]

• tested & fixed some edge cases like stations w/o mounts (HLS-only),
  stations w/ broadcasting or public pages disabled,
  stations w/ no streams at all (no mounts, no HLS),
  stations w/ nothing on schedule.
• fix unneeded abort on some API errors (api.get returns empty list now)
• add api.verify() to check we’re actually accessing an AzuraCast server,
  avoids producing useless files
• other minor code cleanup, unified error messages
• re-arrange #EXTINF for better human readability (Name Group Radio? ID Logo)